Many devices can be used to characterize items of currency. For example, a validation device, comprising a validation unit, can be used to characterize an item of currency.
For the purposes of the disclosure, the term currency and/or item of currency includes, but is not limited to, valuable papers, security documents, banknotes, checks, bills, certificates, credit cards, debit cards, money cards, gift cards, coupons, coins, tokens, and identification papers.
In such state of the art devices the validation unit includes a sensing module often further comprising a source for emitting light and a receiver for receiving the emitted light. Validation of an item of currency can involve the measurement and analysis of one or both of reflected light and light transmitted through a currency item. Additionally, validation can include, but is not limited to, type detection, denomination, validation, authentication and document condition determination.
Some validation units are arranged to use a plurality of light emitting sources (e.g., Light Emitting Diodes (LEDs)) to gather reflective and/or transmission responses from a currency item. Generally these sources are configured such that they emit light within a relatively narrow band of wavelength within a spectrum. More particularly, commonly known sources (e.g., red LEOs, blue LEOs, or green LEOs) typically have an emission spectrum with a narrow bandwidth (e.g., between 15 nm and 35 nm). Examples of common sources can include red sources emitting light in the range of 640 nm to 700 nm, blue sources emitting light in the range of 450 nm to 480 nm, or green sources emitting light in the range of 520 nm to 555 nm. Often such common sources are configured to emit light within wavelength bands consistent with known colors within the visible spectrum (e.g., red light, blue light and green light). The spectral response of a currency item to being illuminated with sources having emission within known color spectrums of visible light can be used to determine various characteristics about the item of currency. In some cases, non-visible light (e.g. infrared, or UV) can be used to gather information about characteristics of an item of currency.
One of the limitations of such a validation unit is that the combination of narrow bandwidth spectrums that are emitted by each individual source may generally result in gaps across the overall spectrum of interest. While it is possible to use a very large number of narrow band sources to cover the overall spectrum of interest, such an approach is undesirable because it could lead to a very large, expensive, and unreliable validation apparatus. Moreover, applying such an approach may increase the frequency of field upgrades to the validation unit hardware to the extent that it becomes desirable to broaden the spectrum of interest after the validation unit has already been deployed to the end-user. In addition, such a solution could result in a device required to process very large amounts of data and thus is not as efficient as required for a currency validation apparatus (e.g., gaming machine, vending, machine, and ticketing machine, etc.) where the validation time interval is critical (e.g., less than one second).
Other image processing machines (e.g., document scanners or photocopiers) use a plurality of sources and detectors to reproduce or store an image of a document. Such image processing machines operate in a way that is analogous to the human eye in the sense that the image processing machine averages the component colors of the document. Thus, similar to the human eye, such image processing machines cannot distinguish between the original document, and the reproduced document image. Such imaging systems can have a high spatial resolution, however the spectral resolution is limited.
Therefore, there exists a need for more efficient, high-performance, reliable, and/or cheaper validation unit.